http://www.sessions.edu/ - Tutorial video from Sessions Online School of Fine Arts' "Drawing" course with NY artist Jordon Schranz.
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To a skilled artist, a bottle is not a bottle, and nor is an apple an apple. Whether they are solid or liquid, all bodies with mass have a form that you can communicate through drawing. Lesson Two deepens your understanding of form, showing you how the elements in your composition can be viewed as fundamental geometrical shapes and objects. You'll also examine the principles of linear perspective, learning about the vanishing point, 1-, 2-, and 3-point perspective, and the phenomenon of foreshortening. Two techniques are addressed to help your integrate these ideas into your work—using measuring points, and using your good ol' thumb as reference. In the exercise, you'll apply all this knowledge to a still life project